Is Ryzen Master safe to use for a beginner?

On the default settings it won't hurt anything. The bit to know is that AMD treats overclocking, including their own auto overclock, as outside the warranty, so read that before you go further. Honestly for a few extra frames I'd skip Ryzen Master and just turn on EXPO for your RAM in the BIOS. On most systems that gives a bigger boost than touching the CPU, and it's what a lot of people forget to do anyway.